This invention relates to a method of and apparatus for rapid forming of a solid three-dimensional article.
Stereolithography (SLA) prototypes are constructed from a liquid photopolymer that is selectively cured using an ultraviolet laser. The process begins with a 3D CAD file which is mathematically sliced into 2D cross sections. With the build apparatus positioned just below the surface of the photopolymer, a scanning system is used to draw the first cross section on the surface of the photopolymer, which adheres to the apparatus.
When the layer is complete, the elevator assembly lowers the apparatus into the vat and the next layer is drawn, with each new layer adhering to the previous one. The process repeats itself until the object is completed. Actual build times can range from under an hour to over a day, depending on the photopolymer, laser power, and the object geometry. Typically, a mechanical blade is used to sweep the surface of the photopolymer to ensure an even layer of resin for the next layer.
One supplier of SLA equipment is 3D Systems, Inc. of Valencia, Calif. Their system is discussed in U.S. Pat. No. 5,885,511. As discussed therein, the apparatus for forming a solid three-dimensional article from a liquid medium capable of solidification when subjected to prescribed energy are known in the prior art. For example, as discussed in the '511 patent, U.S. Pat. No. 4,575,330 to Charles W. Hull discloses a system for generating three-dimensional objects from a liquid medium by irradiating liquid layers with the aid of a computer programmed irradiation source and a translational mechanism.
Conventionally, each object fabricated requires grid-like structures that are attached to downfacing regions of the object (Supports). Supports provide a small, easy-to-remove, break-away region between the stereolithography apparatus (SLA) build apparatus and the object. The use of “sierras” in the construction of Supports minimizes the points of contact between the object and the supports themselves. Removing the supports from the part during Finishing is thereby made easier, and the surface finish of those regions where supports connect to the object, part or model are only minimally affected. If an object were built without supports, as the bottom-most layers of that object were cured by the SLA, solidified resin would become enmeshed in the openings of the SLA's apparatus. This condition would make it difficult-if not impossible-to remove finished parts without damaging them in the process. However, such sierras lengthen the object fabrication time. Moreover, removing the object is still labor intensive with the sierra approach.